Distributed database design refers to the following problem: given a database and its workload, how should the database be split and allocated to sites so as to optimize certain objective function (e.g., to minimize the resource consumption in processing the query workload).

1. Advance Database Management Systems :23
Distributed Database Design
Prof Neeraj Bhargava
Vaibhav Khanna
Department of Computer Science
School of Engineering and Systems Sciences
Maharshi Dayanand Saraswati University Ajmer

2. Slide 25- 2
Distributed Database Concepts
• A transaction can be executed by multiple networked
computers in a unified manner.
• A distributed database (DDB) processes Unit of execution (a
transaction) in a distributed manner. A distributed database
(DDB) can be defined as
– A distributed database (DDB) is a collection of multiple
logically related database distributed over a computer
network, and a distributed database management system
as a software system that manages a distributed database
while making the distribution transparent to the user.

3. Slide 25- 3
Distributed Database System
• Advantages
– Management of distributed data with different
levels of transparency:
• This refers to the physical placement of data (files,
relations, etc.) which is not known to the user
(distribution transparency).

4. Slide 25- 4
Distributed Database System
• Advantages (transparency, contd.)
– The EMPLOYEE, PROJECT, and WORKS_ON tables
may be fragmented horizontally and stored with
possible replication as shown below.

5. Slide 25- 5
Distributed Database System
• Advantages (transparency, contd.)
– Distribution and Network transparency:
• Users do not have to worry about operational details of
the network.
– There is Location transparency, which refers to freedom of
issuing command from any location without affecting its
working.
– Then there is Naming transparency, which allows access to
any names object (files, relations, etc.) from any location.

6. Slide 25- 6
Distributed Database System
• Advantages (transparency, contd.)
– Replication transparency:
• It allows to store copies of a data at multiple sites as
shown in the above diagram.
• This is done to minimize access time to the required
data.
– Fragmentation transparency:
• Allows to fragment a relation horizontally (create a
subset of tuples of a relation) or vertically (create a
subset of columns of a relation).

7. Slide 25- 7
Distributed Database System
• Other Advantages
– Increased reliability and availability:
• Reliability refers to system live time, that is, system is
running efficiently most of the time. Availability is the
probability that the system is continuously available
(usable or accessible) during a time interval.
• A distributed database system has multiple nodes
(computers) and if one fails then others are available to
do the job.

8. Slide 25- 8
Distributed Database System
• Other Advantages (contd.)
– Improved performance:
• A distributed DBMS fragments the database to keep
data closer to where it is needed most.
• This reduces data management (access and
modification) time significantly.
– Easier expansion (scalability):
• Allows new nodes (computers) to be added anytime
without chaining the entire configuration.

9. Distributed database design
• Distributed database design refers to the following
problem:
• given a database and its workload, how should
the database be split and allocated to sites so as to
optimize certain objective function (e.g., to minimize the
resource consumption in processing the query workload).
• There are two issues: (i) Data fragmentation which
determines how the data should be fragmented; and (ii)
Data allocation which determines how the fragments
should be allocated.
• While these two problems are inter-related, the two issues
have traditionally been studied independently, giving rise to
a two-phase approach to the design problem.

10. Defining a Distributed Database
• A distributed database (DDB) is an integrated collection of databases that
is physically distributed across sites in a computer network.
• A distributed database management system (DDBMS) is the software
system that manages a distributed database such that the distribution
aspects are transparent to the users.
• To form a distributed database system (DDBS), the files must be
structured, logically interrelated, and physically distributed across multiple
sites. In addition, there must be a common interface to access the
distributed data.

11. Assignment
• What is a distributed database system
• What are the advantages of Distributed
database system